Adjusting from the objective takes a little longer. You must remember that the yard marks on the objective ring are seldom spot on and clear focus can only be achieved by slowly rotating the ring while focused on a distant target.

The side focus is fast and convenient BUT, sometimes, the precise focus point is a bit difficult to find, and it is necessary to rotate the knob to one extreme, then the other and come back to the point where it is clear. This is called lash in the turrret. I have both types and still prefer the side focus.

Adjusting from the objective takes a little longer. You must remember that the yard marks on the objective ring are seldom spot on and clear focus can only be achieved by slowly rotating the ring while focused on a distant target.

The side focus is fast and convenient BUT, sometimes, the precise focus point is a bit difficult to find, and it is necessary to rotate the knob to one extreme, then the other and come back to the point where it is clear. This is called lash in the turrret. I have both types and still prefer the side focus.

+1

Also the side focus feature is found on 30mm tube scopes allowing larger internals and
normally more MOA adjustments.

The side focus adjustment is just like the focus on a pair of binoculars, you have to go past
focus both ways to find the best distance.

I've got a VX3 6.5-20x40LR with the side parallax adjustment. I've painted a tiny red dot on my side parallax knob to give me a quick ref point easier than the unmarked scale to quickly find my 200 yard parallax free setting. Helps me a lot.

I'm only a year into this gun/scope combo and haven't yet fully stretched its legs but for the ranges I've shot so far (out to 500) I have been unable to detect any lash. Maybe mine is lucky and nice and tight, maybe I'm missing it. But I've tried working with it at different distances and it always comes back spot on for me.

Affects POI. With an incorrect parallax setting if you set your rifle in a stationary rest and move your head around the eyepiece, you will see the reticle move along with your head. With a correct parallax the reticle will be completely stationary. At longer ranges, this deviation gets significant so that if your eye isn't 100% centered in the scope, your reticle is not going to be accurate.

Incidentally... especially noticeable at higher magnifications ... an incorrect parallax setting ALSO causes the image to be slightly out of focus at different distances. So you can "almost" use it as a focus knob which will get you "close" to parallax free. But it is not a focus knob. The whole thing is exacerbated and complicated by some manufactures calling it a focus knob. I think if you use it as a focus knob you will be misleading yourself into thinking your parallax is properly dialed out just because your sight picture is clear enough.